1. Field of Invention
This invention relates to a textile finishing process using aqueous formaldehyde for treating various fabrics including fabrics containing cellulose fibers and fabrics containing protein fibers. The process is also applicable to fabrics containing combinations of these and different fibers, such as synthetic fibers, e.g. polyesters. Textile finishing processes using formaldehyde as a reactive component are well known but suffer from many disadvantages. This invention relates to new textile finishing processes using aqueous formaldehyde, compositions and treated fabrics.
2. Description of Related Art
There are a number of known processes for treating textile fabrics with formaldehyde. The textile fabrics to be treated include those containing protein fibers such as wool and silk. The cellulosic fibers include cotton and rayon. These treatment processes include resin or polymer treatment of the fabric, but these are costly and unsatisfactory. Another process for treating fabrics and particularly cellulosic fiber-containing fabrics is a durable press process which relies on formaldehyde to provide durable cross linking of the cellulose molecules and to thereby impart durable crease resistant and smooth drying characteristics to these fabrics and products containing them. The textile fabrics to be treated are usually cotton/blend fabrics. Other synthetic fibers such as polyesters and the like are often included in these fabrics to provide additional properties. For example, polyester fibers are added to cotton fibers to form cotton/polyester blends. The polyester fibers are added to compensate for the loss in strength of the cotton fibers due to the formaldehyde treatment. Problems have been encountered with the known processes. A simple, reproducible, completely satisfactory low-cost formaldehyde treatment process, particularly, a durable press process has not yet been achieved.
It has long been known to treat cellulosic materials with formaldehyde, as is evidenced by U.S. Pat. No. 2,243,765. This patent describes a process for treating cellulose with an aqueous solution of formaldehyde containing a small proportion of an acid catalyst under such conditions of time and temperature that the reaction is allowed to approach its equilibrium. In carrying out this process, the proportion of the solution of formaldehyde to the cellulose must be at least such that the cellulose is always in a fully swollen state. The time and temperature of the treatment with the solution of formaldehyde and acid catalyst will vary with one another, the time required increasing rapidly as the temperature diminishes. When it is desired, the product may be isolated by washing and drying; preferably at a temperature of about 212xc2x0 F. The products obtained according to this process are said to show no increase in wet strength and possess a high water of imbibition, an increased resistance to creasing and a slight increase in affinity to some direct dyes.
In recent years additional methods have been devised for treating cellulosic fiber-containing products in order to impart durable crease retention, wrinkle resistance and smooth drying characteristics to these products. As discussed, formaldehyde has been cross linked with cellulose materials to produce these products. It is also known to treat cellulose materials with resins or precondensates of the urea-formaldehyde or substituted urea-formaldehyde type to produce a resin treated durable press product. As noted in U.S. Pat. No. 3,841,832, while formaldehyde has made a significant contribution to the cotton finishing art, the result has been far from perfect. For instance, in some cases the formaldehyde cross linking treatment has tended to lack reproducibility, since control of the formaldehyde cross-linking reaction has been difficult. As noted in U.S. Pat. No. 4,396,390, lack of reproducibility is especially true on a commercial scale.
Moreover, unacceptable loss of fabric strength has also been observed in many of the proposed aqueous formaldehyde treatment processes. When high curing temperatures were used with an acid or potential acid catalyst, excess reaction and degradation of the cotton often happened which considerably impaired its strength. On the other hand, when attempts were made to achieve reproducibility at temperatures of 106xc2x0 F. or less, much longer reaction or finishing times were usually required, rendering the process relatively unattractive economically. A solution to this is set forth in U.S. Pat. No. 4,108,598, the entire disclosure of which is herein incorporated by reference. Rayons, e.g. regenerated cellulose (both viscose and cuprammonium) are described in this patent as cellulosic containing fibers as is known to the prior art.
This invention relates to a textile finishing process for treating a textile fabric to impart or enhance at least one property of the fabric. Such properties include durable press characteristics of the fabric and preferably durable press properties are imparted to the fabric while reducing loss of the fabric""s strength during the finishing process. Further properties include a reduction in fabric shrinkage and/or an improvement in the ability for aqueous laundering of the treated fabric. The invention also includes compositions or composites used in the process and the fabrics treated by the processes.
The invention includes a process for treating a textile fabric to impart or enhance at least one property of the fabric comprising introducing the fabric into an aqueous formaldehyde containing solution to provide a wet pickup of an effective amount of the solution by the fabric, applying to the fabric an effective amount of a catalyst for catalyzing a reaction between formaldehyde and the fabric; and exposing the wet fabric to a temperature of at least about 300xc2x0 F. to react the formaldehyde with the fabric to impart or enhance the property of the fabric before there is a substantial loss of formaldehyde from the exposed fabric.
The aqueous solution may be applied to the fabric, preferably, by introducing the fabric into an aqueous solution to provide a wet pickup of an effective amount of the solution by the fabric. In one aspect, the treating solution comprises an effective amount of formaldehyde or formaldehyde generating material and a catalyst for catalyzing a reaction between formaldehyde and the fabric. After this initial application of the aqueous solution, which may be at ambient temperature, the fabric is thereafter exposed to a temperature of about 300xc2x0 F. to react the aqueous formaldehyde with the fabric to impart or enhance at least one property of the fabric before there is a substantial loss of formaldehyde from the exposed fabric. This may be done by introducing the fabric into a heating zone having a temperature of at least about 300xc2x0 F.
The fabric containing cellulosic fibers or protein fibers are reacted with aqueous formaldehyde when an elastomer is present. It is possible to obtain good durable press properties in a cellulosic fiber-containing fabric with good strength retention and consistent results by a durable press/wrinkle-free process for cellulosic fiber-containing fabrics. This process utilizes formaldehyde and catalysts with an elastomer to impart wrinkle resistance to the cellulosic fiber-containing fabrics while reducing loss in both tensile and tear strength. Silicone elastomers are preferred for use in the process. The process is particularly effective on 100% cotton fabrics.
Also included is a process for treating a textile fabric to enhance at least one property of the fabric comprising treating the fabric at ambient temperature with an aqueous formaldehyde solution and catalyst for catalyzing the reaction between formaldehyde and the fabric; and introducing the wet fabric into a heating zone having an elevated temperature of at least about 300xc2x0 F. to subject the ambient temperature-treated fabric directly to the elevated temperature for reaction of the formaldehyde with the fabric to enhance the property of the fabric.
In another aspect of the invention, the process for treating a textile fabric with formaldehyde to enhance at least one property of the fabric comprises treating a fabric containing fibers selected from the group consisting of cellulosic fibers and protein fibers with formaldehyde to react with said cellulosic or protein fibers, and grafting an elastomer onto said cellulosic or protein fibers.
A further aspect of the invention includes a post treatment process to remove excess formaldehyde from the fabric by washing the treated fabric with an aqueous solution of a formaldehyde removing agent which may be an organic acid. Since the concentrations of treating chemicals, including formaldehyde will vary with the fabric being treated, the concentration of the formaldehyde removing agent can be determined by routine experimentation.
The process also includes the use of urea or a derivative thereof to increase the strength of the fabric. The treated fabrics also form part of the invention.
In yet a further aspect of the invention, stable chemical compositions or composites may be used to prepare the aqueous treating solutions for use in the processes of the invention.
The chemical compositions, including water and optional ingredients, which are applied to the fabric in the process may be applied to the fabric together from an aqueous system or sequentially anytime during the process so long as the sequence of addition of the various compositions to the fabric does not prevent the desired level of treatment in the fabric.